[CI] DateHistogramGroupSourceTests.testBackwardsSerialization72 failure

[dimitris-athanasiou]

Build scan: https://gradle-enterprise.elastic.co/s/qqcvgqx5jompo

Repro line:

./gradlew ':x-pack:plugin:core:test' --tests "org.elasticsearch.xpack.core.transform.transforms.pivot.DateHistogramGroupSourceTests.testBackwardsSerialization72" -Dtests.seed=70E39AC50677B868

Reproduces locally?: Yes (with the random seed)

Failure excerpt:

java.lang.AssertionError: expected:<{
      "field" : "yeOfWZiq",
      "script" : {
        "id" : "qXvdh"
      },
      "calendar_interval" : "1M"
    }> but was:<{
      "field" : "yeOfWZiq",
      "calendar_interval" : "1M"
    }>
        at __randomizedtesting.SeedInfo.seed([70E39AC50677B868:467188109FBD3A3A]:0)
        at org.junit.Assert.fail(Assert.java:88)
        at org.junit.Assert.failNotEquals(Assert.java:834)
        at org.junit.Assert.assertEquals(Assert.java:118)
        at org.junit.Assert.assertEquals(Assert.java:144)
        at org.elasticsearch.xpack.core.transform.transforms.pivot.DateHistogramGroupSourceTests.testBackwardsSerialization72(DateHistogramGroupSourceTests.java:75)

[elasticmachine]

Pinging @elastic/ml-core (:ml/Transform)